Chest AP is a radiography positioning projection of the Thorax. Anteroposterior upright chest projection. SID 72". The centering point is located level of t7, approximately 7 inches (18 cm) below the vertebra prominens. cr horizontal and perpendicular to ir.. The central ray is horizontal, perpendicular to ir. centered to t7.. Image-quality criteria include both lungs visualized in entirety, apex to costophrenic angles., a minimum of 10 posterior ribs visible above the diaphragm.. Standard exposure ranges from 110 to 125 kVp, 3 to 8 mAs, at an SID of 72 inches (180 cm).
Anatomy demonstrated
- Entire lungs from apex to costophrenic angle.
- Heart and mediastinum (with greater magnification than PA).
- Thoracic vertebrae and ribs.
- Trachea, carina, and main bronchi.
- Diaphragm and costophrenic angles.
- Clavicles and sternoclavicular joints.
Patient preparation
- Verify patient identity using two identifiers.
- Remove all radiopaque objects from the chest area.
- Confirm pregnancy status for female patients of child-bearing age.
- Explain breathing instructions: inspiration on the second breath in, hold.
- Position patient erect facing the tube, chin raised, shoulders back.
Position & centering point
Level of T7, approximately 7 inches (18 cm) below the vertebra prominens. CR horizontal and perpendicular to IR.
Central ray
Horizontal, perpendicular to IR. Centered to T7.
Exposure / technique
- kVp
- 110–125
- mAs
- 3–8
- SID
- 72" (180 cm)
- Notes
- High-kVp technique. Grid required. AP shows greater cardiac magnification than PA.
Image-quality criteria
- Both lungs visualized in entirety, apex to costophrenic angles.
- A minimum of 10 posterior ribs visible above the diaphragm.
- Sternoclavicular joints equidistant from the spine (no rotation).
- Scapulae rotated laterally and clear of the lung fields.
- Clavicles in a horizontal plane, projecting just above the lung apices.
- Sharp diaphragm and vascular markings (no respiratory motion).
- Trachea visible in the midline, sternum superimposed by the spine.
Common errors / ARRT traps
- 1 Excessive shoulder elevation tilts the mediastinum and obscures the apices.
- 2 Rotation of the body shifts one clavicle laterally off the midline.
- 3 Chin not raised enough causes superimposition of mandible over apices.
- 4 Inadequate inspiration reduces rib visibility and flattens the diaphragm.
- 5 Off-centered CR clips the lung apices or costophrenic angles.
Clinical indications
- Routine evaluation when PA positioning is not feasible.
- Trauma or acute care settings with portable equipment.
- Follow-up studies after interventions.
- Comparison with prior PA studies.
Aligned to the 2025 ARRT Content Specifications.